The field of art of which the invention pertains includes steering mechanism, and more specifically steering mechanism for industrial lift trucks and other vehicles.
Prior steering mechanisms, particularly for vehicles of the type primarily contemplated, have more or less successfully coped with several problems inherent in the design of such mechanisms, and predictably there have been several prior design approaches.
One of the problems encountered and not fully resolved heretofore has concerned the provision of a steering geometry in a four wheeled vehicle capable, within a relatively confined space, of producing substantially ideal differential steering angles as between the dirigible wheels through a very wide range of angular movement of the wheels, such as 180.degree. from a full right cramp to a full left cramp position thereof. A typical prior steering mechanism for a lift truck using a four-bar linkage design is disclosed in Howell U.S. Pat. No. 2,191,961, which includes a rather full explanation of the theory of differential angular steering such that the wheels roll with relatively little lateral slip or scuffing during turning maneuvers of the truck.
Another problem has been to provide in the limited space ordinarily available for steering such trucks a steering linkage and tie bar assembly which is effective with a relatively small variation in actuator force to turn the steering wheels to a high angle full cramp position. Heretofore the effective turning moment arm has approached a very small value at high maximum steering angles in conventional four-bar steering mechanisms, thereby requiring either a relatively large range of actuator force or a substantial limitation on steering angle. Prior steering mechanisms of the type contemplated have not been available to provide 180.degree. steering angles combined with accurate steering geometry.
While some prior steering axles, such as shown in Gaulke U.S. Pat. No. 3,480,100 and Matteo U.S. Pat. No. 3,768,585, have utilized a combination power actuator and tie rod construction, they are unable to effect 180.degree. wheel swing with accurate steering geometry in a relatively small space.